After the financial crisis, housing regulators worked to prevent banks and other interested parties from pressuring real estate appraiser to inflate valuations. The only problem is, it might not have worked. Per Bloomberg:

Since the housing boom ended, mortgage volume has dropped by two-thirds and home sales are still about 30 percent below the 2005 peak. Meanwhile, the number of licensed and certified appraisers, now about 100,000, has fallen at only half the rate of home sales and much less than the drop in mortgage-origination volume. The result is an oversupply of appraisers, with more of them willing to come up with valuations to make a transaction work.

The article explained that this combination is why an estimated one in seven appraisals is inflated by as much as 20%.

Be sure to check the article for a helpful graph that puts it into better perspective.